La environmental contingency due to ozone in the Valley of Mexico It has once again brought the air quality of one of the world's largest urban areas into sharp focus. For several consecutive days, warnings, traffic restrictions, and health recommendations were issued, with particular attention given to the most vulnerable groups.
Throughout this episode, environmental authorities activated and subsequently suspended the Phase I of environmental contingency in the Metropolitan Area of the Valley of Mexico (ZMVM), according to the evolution of weather conditions and pollution levels. The case serves as a reference for other large cities, including European ones, that face similar problems. tropospheric ozone, heavy traffic and episodes of atmospheric stability.
How and why was Phase I of the ozone contingency plan activated?
According to official information from Megalopolis Environmental Commission (CAMe)Phase I was declared after a maximum concentration of 160 parts per billion (ppb) of ozone at the Cuajimalpa monitoring station, west of the Valley of Mexico, around 16:00 p.m. on a Thursday in January.
CAMe explained that the region was under the influence of a high-pressure system in the center of the country, which led to Mostly clear skies, hazy atmosphere, few clouds, intense solar radiation, and very weak windsThis combination resulted in a strong atmospheric stability, promoting the accumulation of ozone precursors and the pollutant itself.
The Commission itself detailed that the stagnant air within the Valley of Mexico This contributed to the increase in ozone concentration during the afternoon, as there was insufficient ventilation to disperse the pollutants. This was compounded by unusually high temperatures for this time of yearwhich were around 25 ºC, a factor that also intensifies the photochemical processes that generate ozone from other pollutants emitted, above all, by road traffic and industrial and domestic activity.
The decision to activate Phase I had as its main purpose reduce the population's exposure to polluted air and minimize the risk of health problemsas well as curbing, as far as possible, the emissions that contribute to ozone formation. In European contexts, these types of episodes are monitored similarly, with action thresholds, public warnings, and temporary traffic restrictions when certain levels are exceeded.
Air quality, vulnerable groups and health recommendations
During the episode, the Mexico City Atmospheric Monitoring System He warned that air quality would be in the range of Bad to Very Bad in several areas of the Valley of Mexico, especially during the middle of the day. It was indicated that the worst time for outdoor exposure would be between 13: 00 and 19: 00 hours, a band in which ozone peaks are usually reached.
The authorities insisted that the higher risk groups They needed to take extreme precautions: children, the elderly, pregnant women, and those suffering from respiratory or cardiovascular diseasesFor all of them, it was recommended to avoid prolonged exposure outdoors, especially during that time of peak concentration.
The official statements included a package of health and lifestyle recommendations, which included:
- Avoid outdoor civic, cultural, recreational, and sporting activities between 13:00 p.m. and 19:00 p.m.
- Suspend or postpone massive outdoor events, both organized by public and private institutions.
- Do not perform intense outdoor physical exercise during the hours of worst air quality.
- No Smoking, especially in enclosed spaces, to avoid increasing exposure to pollutants.
- Consult the air quality reportsthrough mobile applications or official monitoring systems.
In the domestic sphere, the importance of reduce emissions within homeslimiting the use of products that release volatile organic compounds, such as aerosols, solvents, paints, air fresheners, and waterproofing agents. It was also recommended reduce hot water consumption (for example, by shortening shower time) and using covered containers when cooking to optimize fuel use.
Measures to cut emissions: housing, mobility and fuels
Beyond health recommendations, environmental authorities proposed concrete measures to reduce emissions of ozone precursors during the emergency. Among the general proposals was the possibility of facilitate remote work wherever feasible, with the aim of reducing the number of daily journeys and, consequently, traffic and fuel use.
Emphasis was also placed on avoiding domestic or professional tasks that involve intensive use of volatile chemicalsThese include substances such as certain paints, solvents, waterproofing agents, and aerosols. These compounds react in the atmosphere under strong solar radiation and contribute to the formation of tropospheric ozone, a secondary pollutant that is not emitted directly but is generated in the air itself.
Another area of action was that of the fuels for vehicles and heatingIt was recommended:
- Fill up with gas preferably after 18:00 p.m. or before 10:00 a.m., to reduce evaporative emissions during critical hours.
- review the domestic gas installations to prevent leaks, which, in addition to being a safety risk, represent an additional source of emissions.
- Reduce fuel consumption at home, adjusting heating and hot water to what is strictly necessary.
In the specific case of fuel distribution, specific restrictions were introduced: the following were considered: 50% reduction in the circulation of LP gas delivery units that did not have a dry disconnect valve and had license plates ending in an even number, a type of measure similar to those being considered in Europe for intensive transport fleets during pollution episodes.
Today's No Driving program has been reinforced: affected vehicles and exemptions
As is the case in other instances of poor air quality, one of the cornerstones of the response was the Strengthening the Hoy No Circula program in Mexico City and the State of Mexico. The activation of Phase I involved extended restrictions on vehicle traffic during the Friday following the declaration of the contingency.
By that day, among the 5: 00 and 22: 00 hoursThey had to stop circulating:
- Private vehicles with verification hologram 2.
- Vehicles with hologram 1 whose last digit of the registration was 2, 4, 6, 8, 9 or 0.
- vehicles with hologram 0 and 00, blue sticker and license plate ending in 9 and 0.
- Cars without holograms, with foreign license plates, tourist passes, or license plates consisting only of letters, were treated for control purposes as hologram 2.
El local and federal freight transport It was also subject to limitations: in general, its circulation between the 6: 00 and 10: 00 hoursexcept for units included in specific self-regulation programs. In parallel, the following were established specific restriction hours for taxis with holograms 0, 00, 1 and 2, applied mainly from 10:00 to 22:00, with the idea of maintaining some mobility capacity without excessively increasing emissions.
The exemptions included the Electric and hybrid vehicles, motorcycles, emergency units (ambulances, fire trucks, police), authorized school transport, vehicles for people with disabilities and certain essential urban servicesThe logic behind this approach, shared with many European cities, is to prioritize the mobility of critical services and, at the same time, incentivize less polluting technologies.
Suspension of the contingency: winds improve and the high-pressure system moves away
Following the tightening of measures, the evolution of the atmospheric situation allowed the Megalopolis Environmental Commission to decree, already on Friday afternoon, the suspension of the ozone contingency in the Metropolitan Area of the Valley of Mexico. The key change occurred starting at 16:00 p.m., when a decreased atmospheric stability and an increase in windfactors that favored the dispersion of pollutants.
According to the reports, ozone levels were descending continuously until it falls within the normThis opened the door to lifting Phase I restrictions starting at 18:00 PM that same day. It was anticipated that by the following Saturday... high-pressure system moved away from the Valley of Mexico, creating better conditions for ventilation and the removal of pollutants from the basin.
The suspension of the contingency also meant the end of the extraordinary restrictions of Hoy No CirculaIt was announced that the program would resume operating under its usual scheme, without the expansions typical of Phase I. Despite this, authorities stressed the need to maintain good practices to limit emissions, aware that similar episodes could be repeated when unfavorable weather conditions coincide.
Other recent incidents and the importance of continuous monitoring
The ozone episode described was not an isolated incident. CAMe recalled that another contingency had already been declared earlier in the year. southeast of the Valley of Mexicoalthough on that occasion it was mainly linked to fine particles PM2.5That day, the monitoring system recorded concentrations around 107,3 micrograms per cubic meter, well above the values recommended by the World Health Organization (WHO), which suggests a maximum exposure of 10 micrograms per cubic meter in 24-hour averages.
In that previous episode, the main source of the pollution was related to the intensive use of fireworks and the burning of materials and fuels during the New Year's celebrations. Although the emergency was lifted that same afternoon, the case once again illustrated the Vulnerability of the Valley of Mexico to episodes of poor air quality and the need to coordinate rapid measures between different levels of government.
During the recent ozone crisis, the CAMe, the Ministry of Environment and Natural Resources and the environmental authorities of the capital and the State of Mexico committed to issue update bulletins at specific timessuch as 15:00 PM or 20:00 PM, or even earlier if conditions required it. This regular communication allows the public to adjust their routines and plan journeys, something increasingly common in large European cities as well, where air quality monitoring systems are a key urban management tool.
This episode of environmental contingency due to ozone in the Valley of Mexico It shows how the combination of adverse weather conditions, heavy traffic, and diffuse emissions can quickly lead to pollution levels that necessitate exceptional measures. The activation and subsequent lifting of Phase I, mobility restrictions, public recommendations, and constant air quality monitoring reflect a course of action that, with some variations, is also observed in many metropolitan areas across Europe, where combating ozone and particulate matter remains one of the major challenges of environmental and public health policy.
